The family Lauraceae, a hyper-diverse magnoliid family comprising approximately 63 genera and over 3,000 species, plays a key ecological role in tropical and subtropical forests. Yet deep relationships among its nine tribes remain unresolved, likely due to limited sampling and complex evolutionary processes such as incomplete lineage sorting (ILS) and gene flow. To address these challenges, we generated datasets of 255 single-copy nuclear genes and chloroplast genomes using a newly designed Lauraceae-specific probe set, achieving the most comprehensive genus-level sampling (84%) to date. Phylogenomic analyses reconstructed a robust nuclear tree, which resolved the Neocinnamomeae as sister to the Caryodaphnopsideae and revealed pronounced gene tree conflict and pervasive cytonuclear discordance. To investigate the evolutionary processes underlying these patterns, comprehensive analyses were conducted. The results indicate that conflicting nuclear gene trees reflect the combined effects of ILS, gene tree estimation error, and gene flow, with ILS dominating across the core Lauraceae, whereas cytonuclear discordance is primarily driven by extensive gene flow. Diversification analyses further indicate that episodes of rapid lineage accumulation coincide with major gene flow events, suggesting a potential role of gene flow in the diversification of Lauraceae. Overall, this study provides a robust nuclear phylogenomic framework for Lauraceae and demonstrates that gene flow had profound effects on its evolutionary history, shedding light on the contribution of gene flow to the diversification of hyper-diverse tropical plant lineages.
Ribosomal ITS2 is widely used in phylogenetic studies, yet its multigene organization and potential paralogy can obscure true species relationships. This proof-of-concept study investigates whether ITS2 sequences derived from long-read genomic data in multiple Xiphophorus species primarily reflect orthologous history or are shaped by ancient and local duplications. Phylogenetic analyses reveal two major, reciprocally mirroring ITS2 clades that represent long-standing paralogous rDNA lineages rather than simple allelic variants. The two paralogons show strong asymmetry in copy retention and loss for the majority of the species analyzed in this study. Exceptionally some other species are confined to one paralogon group and exhibit alternating ITS2 variants consistent with persistent ancestral polymorphism. A striking copy number imbalance in X. variatus, combined with its phylogenetic incongruence relative to the established species tree, is best explained by historical rDNA introgression followed by biased concerted evolution that nearly erased one paralogous copy. Despite incomplete homogenization, heterogeneous evolutionary rates, and occasional long-branch artifacts, the recovered paralog-specific topologies largely recapitulate the accepted Xiphophorus species phylogeny, indicating that ITS2 retains a robust organismal signal while also recording episodes of introgression and differential paralog evolution. These results demonstrate that explicit recognition of ITS2 paralogs can both improve phylogenetic interpretation and open avenues for future sequence-structure-based analyses of rDNA evolution and genus-level systematics in Xiphophorus.
Ciliates are an excellent model for studying convergent transitions from mitochondria to mitochondrion-related organelles (MROs) in protists. Despite our growing knowledge of adaptive evolution in ciliate MROs, the progressive evolutionary trajectories within anaerobic ciliate lineages and the MRO metabolisms of facultatively anaerobic ciliates remain unexplored. In this study, we predicted MRO metabolisms of eight species within the anaerobic monophyletic APM (Armophorea, Parablepharismea, Muranotrichea) clade and a facultative anaerobe from its sister class Spirotrichea. Our main results are as follows: (1) During their adaptation to anaerobic environments, the MRO electron transfer chain (ETC) components and their associated functions have been progressively lost in the APM clade. (2) The MRO of the last common ancestor of Armophorea likely possesses complexes Ⅰ, Ⅱ, and Ⅴ, but lacks functional complexes Ⅲ and Ⅳ. Subsequently, during their adaptation to anaerobic environments, the armophorean lineage has further lost complex Ⅴ in the order Clevelandellida and Metopida. (3) In the MRO of the facultatively anaerobic ciliate Heterodeviata sinica, complexes Ⅲ and Ⅳ are absent, and alternative oxidases (AOX) play a key role in adaptation to fluctuating dissolved oxygen levels. (4) The fused [FeFe]-hydrogenase appears to have been acquired by the last common ancestor of ciliates through horizontal gene transfer (HGT), followed by multiple independent losses. Our results provide insights into the progressive adaptations of anaerobic ciliates to the low-oxygen environments.
Paramecium bursaria maintains a stable endosymbiosis with green algae, yet the evolutionary consequences of this association remain unclear. Here, we screened the host genome for algal-derived horizontally transferred genes (HTGs) using a lineage-aware workflow designed to detect horizontal gene transfer (HGT) between two defined lineages. We identified 16 candidate HTGs, including four putative newly transferred genes and 12 homologous transferred genes, most of which were functionally associated with redox homeostasis and metabolism. Five HTGs showed symbiosis-dependent expression. RNAi knockdown of GH32s and SATs reduced host proliferation, total cell area, and motility, while GH32s knockdown also reduced endosymbiont load. Duplication patterns suggest that most transfers may have occurred after the P. bursaria lineage diverged from the sampled Paramecium species but before its lineage-specific whole-genome duplication (WGD). The HTGs also showed host-associated shifts in GC content and gene length, while representative HTGs retained conserved domains and functional motifs. Together, our results support algae-to-host HGT in P. bursaria and suggest that some transferred genes may contribute to metabolic integration during endosymbiosis.
The mechanisms driving lineage divergence in red algae remain unexplored, despite the group's remarkable diversity and ancient evolutionary history. The red alga Mazzaella laminarioides, a Chilean intertidal species complex composed of three parapatric cryptic lineages (North, Center, South), offers a valuable system to evaluate these processes, as its life history combines severe dispersal limitation with a haploid-diploid cycle that may influence the emergence of reproductive barriers. We reconstructed its evolutionary history using whole-genome sequencing and nuclear genome assembly of representative individuals from each lineage. Phylogenomic analyses based on 1,507 single-copy orthologs recovered three deeply divergent lineages with limited nuclear discordance consistent with incomplete lineage sorting. For both splits, demographic modelling was most consistent with an Ancient Migration scenario, although support over strict isolation was moderate, suggesting that divergence may have begun with low asymmetric ancestral gene flow followed by subsequent loss of connectivity, demographic bottlenecks, and later population expansion. Coding sequence analyses revealed lineage-specific dN/dS heterogeneity; only one South-lineage locus passed FDR correction (metaxin-1, mitochondrial protein import), with two further South-lineage candidates in chlorophyll and heme biosynthesis falling below the FDR threshold. Together, these signals suggest that divergent selective pressures on energy acquisition may have contributed to divergence at the southern end of the distribution. These results add to the small but growing body of whole-genome data for red algae and, alongside recent macroalgal studies, suggest that ancestral connectivity could be a recurrent feature of lineage divergence even in marine organisms with extremely restricted dispersal.
Diervilleae (Caprifoliaceae) is a horticulturally important lineage with striking floral diversity and a long history of interspecific crossing, suggesting reticulate evolution. We integrated nuclear SNPs and whole plastome data to reconstruct a phylogenomic backbone for the tribe and to identify hybrids, cultivated accessions, and introgression among lineages. Nuclear and plastid phylogenies consistently recover Weigela and Diervilla as reciprocally monophyletic and resolve four major lineages within Weigela, providing a reproducible framework for revising sectional limits and species boundaries. Cultivated accessions form a well supported clade sister to W. florida and show predominantly W. florida ancestry while retaining contributions from multiple wild lineages, consistent with recurrent crossing, backcrossing, and selection. Analyses of wild populations reveal recurrent hybrids and enable plausible parental combinations to be inferred. Tests across the genome further indicate strong evidence for historical introgression across Diervilleae, with the strongest signals involving W. middendorffiana, W. maximowiczii, and Diervilla. Fossil evidence, divergence time estimation, and paleodistribution modelling together suggest range expansion during the Miocene and Pliocene followed by climate driven contraction, providing a spatiotemporal context for episodic contact, introgression, and the East Asia-North America disjunction.
Antipatharians (black corals) are among the least studied coral groups, with much of their diversity still undescribed. Here, we present an integrative morphological, phylogenomic and genomic distance study of deep-sea antipatharians sampled in high seas areas of the North Pacific Ocean and from New Zealand’s Exclusive Economic Zone. These corals grow on hexactinellid sponges — a unique characteristic in the order Antipatharia. Using a dataset of ultra-conserved elements and exons, combined with morphological analyses, we reconstruct phylogenomic relationships and formally describe a new family (Eidikopathidae fam. nov.), a new genus (Eidikopathes gen. nov.), and two new species (E. korallispongia sp. nov., E. zealandkorallia sp. nov.). Morphologically, the new family is distinguished by a corallum consisting of a network of loose branches that fuse with the sponge skeletal framework. Phylogenomic analyses recovered consistent topologies with strong nodal support, corroborating the distinct evolutionary placement of this sponge-associated lineage. Pairwise genomic distances estimated using the Tamura-Nei model were concordant with patristic genomic distances, identifying Pteridopathidae as the genetically closest family to Eidikopathidae fam. nov., followed by Myriopathidae and Stylopathidae, which were recovered as sister families in the phylogeny. This pattern shows that genomic distance complements, rather than simply mirrors, tree topology by quantifying accumulated sequence divergence among lineages. Together, these results provide the first genomic distance framework for Antipatharia, offering a baseline for future systematic, evolutionary, and biodiversity studies on this fundamental shallow, mesophotic and deep-sea coral group.
The angiosperm order Rosales still represents a major challenge for phylogenetic reconstruction. Although its circumscription is now well-defined, phylogenetic relationships among families are still uncertain. Here, we used nuclear, plastid, and mitochondrial genomic data from 33 species representing all nine families to further clarify interfamilial relationships and the group’s evolutionary history. We detected significant phylogenetic conflict among the three datasets. Further analyses at the nuclear level identified incomplete lineage sorting (ILS) as the main cause of unstable phylogenetic positions among families. The discordant placements of Rhamnaceae and Elaeagnaceae based on plastid and mitochondrial data are caused by ancient hybridization events, potentially involving differences in organellar inheritance. Our molecular dating confirms earlier suggestions that the ancient rapid diversification of the three Rosaceae subfamilies could be the main reason for the difficulties in resolving their phylogenetic relationships. Our findings provide new insights into the interfamilial relationships of Rosales and demonstrate that the evolutionary history of this order was shaped by ancient and rapid radiation as well as extensive ILS and reticulate evolution. They also suggest that previous attempts to clarify interfamilial relationships in this order were hampered by combining nuclear and organellar sequence data, leading to inconsistent topologies observed across earlier studies.
Understanding how lineages diversify despite persistent ancestral polymorphism and recurrent gene flow remains a central challenge in evolutionary biology. Juniperus distributed across the Qinghai-Tibet Plateau provide an ideal system for addressing this question because repeated geological uplift and climatic oscillations have likely promoted cycles of lineage divergence, range shifts, and secondary contact. Here, we combined approximately 1.08 million genome-wide SNPs from 164 individuals representing thirteen Juniperus lineages with phylogenomic datasets comprising 3,381 nuclear single-copy genes and nearly complete plastomes. We detected extensive phylogenomic discordance and cytonuclear incongruence across genomic datasets. Topology weighting, coalescent simulations, quartet-based tests, and analyses of gene flow and reticulation collectively support the interpretation that these patterns were shaped by the combined effects of prolonged incomplete lineage sorting and gene flow during lineage diversification. Ecological niche analyses further provide a spatial and climatic context in which environmentally similar lineages may have had greater opportunities for secondary contact during historical range shifts. Collectively, our results reveal that the evolutionary history of Qinghai-Tibet Plateau Juniperus is characterized by reticulate diversification rather than strictly bifurcating evolution, and demonstrate how genome-wide discordance can provide biological insights into the evolutionary processes underlying lineage diversification.
The red algal order Halymeniales (Rhodophyta) exhibits remarkable morphological and taxonomic diversity but its higher-level relationships remain poorly resolved. Here, we present a comprehensive phylogenomic analysis based on newly generated plastid (170 protein-coding genes), mitochondrial (23 genes), and complete nuclear ribosomal cistron sequences from 56 taxa, complemented with an expanded rbcL dataset encompassing 334 sequences. Our results provide a robust phylogenomic framework for the Halymeniales, offering a taxonomic backbone for future systematic studies. The analyses consistently recover six early-diverging lineages (Acrodiscus, Isabbottia, Norrissia, Pachymenia, Zymurgia, and Tsengia) and two strongly supported larger clades (Halymenia s.l. and Grateloupia s.l.). While most small and recently described genera are monophyletic, several traditional genera (e.g., Halymenia, Cryptonemia, Grateloupia) are poly- or paraphyletic, requiring considerable taxonomic revision. At the family level, the data indicate that reinstatement of the Grateloupiaceae sensu Kim et al. (2021) would entail a revised circumscription of the Halymeniaceae and the recognition of at least five small families to accommodate the early-diverging lineages. Although such a revised classification would result in monophyletic families, it is not supported by morpho-anatomical characters. Instead, we propose a more stable two-family system, recognizing a broadly circumscribed Halymeniaceae that is sister to the Tsengiaceae. Female reproductive characters, particularly the structure of carpogonial and auxiliary cell ampullae, support this two-family system and further characterize many genus-level clades, although substantial convergence across lineages exists.
Fine-resolution information on species relationships and biological diversity is critically needed to guide conservation efforts amidst rapid environmental changes. Systematics, which forms the foundation of this knowledge, has been revolutionized by phylogenomics, utilizing genome-scale datasets. However, the use of diverse marker types, non-comparable taxon sampling, and outgroup selection can lead to conflicting phylogenetic hypotheses. These inconsistencies complicate study comparisons and hinder our ability to assess marker-specific impacts on phylogenetic resolution. The phylogenetic reconstruction of the bat genus Myotis, encompassing over 140 species and characterized by a rapid radiation in the last 20 million years, has been particularly influenced by these challenges. Achieving phylogenetic resolution in Myotis is particularly complex due to subtle interspecific differences in both morphological and molecular traits. Mitochondrial and nuclear markers often produce discordant trees, influenced by hybridization, introgression, and methodological variations. In this study, we employed a consistent taxonomic sample set of 44 Myotis taxa to evaluate the impact of five different genetic marker types on phylogenetic reconstruction. We observed significant discordance between topologies derived from conserved nuclear and mitochondrial markers and found that transposable elements were inadequate for resolving relationships across the entire genus. Our results also clarify the placement of previously problematic taxa within the genus. These findings emphasize the importance of aligning genetic marker choice with specific phylogenetic questions and highlight the influence of taxonomic and methodological variation on phylogenomic outcomes. This work provides a framework for improving phylogenetic inference in rapidly radiating groups and enhances our understanding of evolutionary history in Myotis.
The expansion of arid and dry ecosystems during the Miocene played a key role in the diversification of succulent plants; however, the relative contributions of biotic traits and environmental factors linked to aridity remain unclear. We investigate diversification in the cactus tribe Cereeae by integrating phylogenomic, biogeographic, and trait-based diversification analyses. We reconstructed a time-calibrated phylogeny and inferred ancestral ranges through biogeographic process-based modeling. We assessed diversification rate heterogeneity and evaluated the impacts of biotic traits and environmental variables using machine learning and trait-dependent diversification analyses. Our results indicate that Cereeae diverged in the late Miocene (∼9 Ma), with ancestral range spanning from the Central and Southern Andes to Espinhaço Mountain Range in Southeastern Brazil. Vicariance events, likely driven by marine transgressions and the assembly of the Cerrado savanna, promoted isolation of taxa across the Andes and Southeastern Brazil. Eastern Brazil was recolonized via jump dispersal during the Miocene-Pliocene transition. Diversification rates were strongly associated with rupicolous substrate preference and globose growth form, while environmental variables showed a negligible correlation with diversification. Our findings underscore the Southern Andes as a likely source of xerophytic lineages and highlight ecological specialization as the dominant driver of Cereeae radiation. This study demonstrates how integrative approaches can disentangle complex evolutionary processes, revealing that morphological innovation prevailed over environmental filtering in shaping the diversification of Cereeae in dry habitats.
Phylogenomic discordance is widespread across plants, but its evolutionary significance is often obscured when conflict is treated primarily as analytical noise rather than as evidence of underlying processes. In woody lineages in particular, incomplete lineage sorting, introgression, and genome duplication can interact over long timescales to produce complex genomic histories that are not adequately summarized by a strictly bifurcating tree. Here, we use Malus as a model woody genus to investigate how these processes structure conflict across a genus-scale, accession-based phylogenomic framework. Using broad taxon sampling, hundreds of nuclear loci, plastid genomes, and genome-wide SNP summaries, we reconstruct a robust nuclear backbone for sampled Malus lineages and evaluate where discordance is concentrated and which processes best explain it. Nuclear analyses resolve eight major clades, whereas conflict is non-random and localized to recurrent hotspots rather than evenly distributed across the tree. Cytonuclear discordance is similarly concentrated, especially around Clade H, represented by sampled accessions of M. tschonoskii, where localized plastid-nuclear disagreement is consistent with candidate plastid capture or organellar introgression. Multiple complementary analyses further indicate that the strongest conflict is not explained by ILS alone, but instead reflects lineage-structured introgression, while polyploid complexes represent additional localized sources of evolutionary complexity. Together, these results provide evidence for a reticulate genomic backbone in Malus and show how integrating nuclear, plastid, and genome-wide conflict analyses can help distinguish background discordance from process-specific signals in woody plant radiations. Several lineage-level reticulation hypotheses identified here should now be tested with broader population-level sampling and curated reference accessions.
Target capture is a common method of generating high throughput DNA sequencing data for phylogenetic reconstruction of species relationships, for which single copy genes are usually most informative. However, a pervasive problem with target capture is that putatively single copy genes may in fact be paralogs resulting from gene duplication, which are problematic for phylogenetic inference because their evolutionary history may differ from the divergence history of species. Here, we use as a case study a target enrichment dataset of 88 species of Detarioideae (Leguminosae) with a focus on the Sindora clade to examine approaches for handling paralogs, including the built-in paralog handling functions in HybPiper and CAPTUS, plus subsequent steps using Putative Paralog Detection and the tree-based Yang & Smith orthology inference approach. We compare the paralogs flagged using these methods and verify their performance with BLAST mapping against a reference genome sequence of Sindora glabra, and then subsequently compare the species tree topologies produced across these methods. Our comparisons of paralogs flagged across the Sindora clade show that the Putative Paralog Detection pipeline was the most accurate in identifying paralogs in terms of its similarity to the BLAST mapping, followed by the built-in paralog identification function of CAPTUS. However, the results we recovered for the Detarioideae subfamily suggest that the largest differences in species tree topology resulted from the use of paralog-filtered alignments (such as with the Putative Paralog Detection pipeline and the Yang & Smith orthology inference approaches) rather than just by removing the sequences of identified paralogous genes. This was the true for HybPiper-assembled datasets but was not seen in CAPTUS-assembled datasets. In all comparisons, the topological differences caused by different paralog handling methods tended to be confined to clades where processes such as hybridisation and introgression are prevalent. Our study provides a roadmap to establish the best approach to identify, eliminate or separate paralogs in the absence of a chromosomally contiguous reference genome for a study group, and highlights the importance of careful data inspection and processing in addition to understanding the extent of paralogy and paralog characteristics (e.g. sequence divergence between copies) for their study group.
The generic-level classification of the bee tribe Megachilini (Megachilidae) has remained controversial due to poor phylogenetic resolution at the base of the group, particularly among the brood parasitic genera and the numerous dauber ("Chalicodoma s. l.") lineages. We present a phylogenomic analysis of Megachilini based on ultraconserved elements (UCEs), sampling 52 ingroup taxa with emphasis on the dauber lineages. We also present a combined UCE + six-gene analysis to improve taxon coverage, resulting in a dataset with 127 ingroup taxa. Maximum likelihood, coalescent, and Bayesian analyses of multiple UCE matrices recover largely congruent topologies with substantially improved support relative to previous studies. Our results strongly support the monophyly of Megachilini, the early divergence of Noteriades and Gronoceras, and a single origin of brood parasitism. All remaining non-parasitic Megachilini form a moderately supported clade sister to the brood parasitic lineage. The leafcutter bees are monophyletic and nested within dauber lineages. Several major dauber clades are consistently recovered, including an exclusively Australian clade corresponding to the Hackeriapis group of subgenera, while several recognized subgenera are paraphyletic. The lineage known as Morphella, previously placed in synonymy with the subgenus Callomegachile, was not closely related to that subgenus and is here treated as a valid subgenus. Divergence-time analyses place the crown age of Megachilini in the late Eocene to early Oligocene, with major extant lineages diversifying during the Miocene. Limited morphological diagnosability of several clades indicates that splitting non-parasitic lineages into numerous genera would result in an impractical classification that would widen the gap between taxonomists and non-specialists and exacerbate the taxonomic impediment in bees. We therefore advocate retaining a single genus Megachile for non-parasitic Megachilini (excluding Noteriades and Gronoceras), as the classification best supported by phylogenomic evidence and most robust to future taxon sampling.
Eunicid polychaetes are often found in association with Cold Water Corals (CWCs), even establishing symbiotic relationships, such as those described between Desmophyllum pertusum and Eunice norvegica. While genetic connectivity of CWCs across the North Atlantic has been widely studied, little is known about their associated fauna in this regard. Here, we present a study combining a focused analysis of the genetic and genomic connectivity of E. norvegica with a regional assessment of the distribution and evolutionary relationships of three CWC-associated eunicid species from the Cantabrian Sea and the North of the United Kingdom (190-1,230 m depth). An integrative approach using genetic (16S, COI and 18S), morphological and ecological data allowed the identification of the eunicids studied, with new records of Eunice cf. nicidioformis and Leodice cf. antarctica in the Cantabrian Sea, as well as previously undocumented associations with CWC species. In addition, RADseq data contributed to the delimitation of the closely related species E. norvegica and Eunice philocorallia. Moreover, the genetic connectivity of E. norvegica was studied trough a RADseq (1,067 neutral SNPs) approach. Our results indicate a single panmictic population across approximately 2,000 km, suggesting that oceanographic currents facilitate passive dispersal of E. norvegica lecithotrophic larvae, aided by coral host stepping-stones. The connectivity patterns observed for E. norvegica mirror those of D. pertusum, on which the worm is ecologically dependent. Our study highlights the importance of using integrated genetic, morphological and ecological data to characterise and delineate understudied CWC-associated species and improve our understanding of their dispersal capabilities and genetic connectivity to inform future conservation recommendations.
Resolving species relationships in rapidly radiating lineages remains a major challenge in evolutionary biology, particularly when hybridization obscures phylogenetic signals. Here, we present a chromosome-level, haplotype-resolved genome assembly for Triplophysa pseudoscleroptera, a species residing at the Qinghai-Tibet Plateau, and integrate it with eight other Triplophysa genomes and resequencing data from 57 Triplophysa individuals to reconstruct a robust phylogeny of the genus. We uncovered extensive discordance between mitochondrial and nuclear phylogenies, driven by both ancient and recent introgression. Notably, the individual selected for genome assembly was found to have undergone a recent hybridization event, retaining ∼ 22% introgressed genomic segments. These introgressed segments are phylogenetically closer to T. dalaica, and their inclusion in concatenated whole-genome alignments was sufficient to mislead species tree inference. Empirical genomic resampling analyses demonstrate that as little as 14% introgression is sufficient to result in incorrect phylogenetic inference in our focal system. Our findings provide a cautionary example that reliance on a single individual genome can lead to erroneous phylogenetic conclusions, when a moderate proportion of introgressed segments is present. We therefore advocate chromosome-scale and window-based phylogenomic approaches as essential practices for reconstructing species relationships in systems shaped by reticulate evolution.
The pantropical genus Diospyros L. (Ebenaceae) includes many economically valuable species prized for ebony timber and edible fruits. However, its high species diversity and morphological similarity pose significant challenges for understanding its evolutionary history. Previous phylogenetic studies have suggested a rapid adaptive radiation in Diospyros, but relationships among major lineages remain poorly resolved. Here, we reconstruct a comprehensive species-level phylogeny for Chinese Diospyros using whole genome sequencing data from 69 individuals representing 65 species. Phylogenomic analyses of a concatenated nuclear SNP matrix recovered six strongly supported major clades. Notably, we found substantial cytonuclear discordance between nuclear and plastid phylogenies. To investigate this conflict, we conducted extensive gene-tree concordance analyses (Phytop, MSCquartets) and quantified introgression and incomplete lineage sorting (ILS) using Dsuite, QuIBL, and PhyloNet. These analyses revealed widespread, statistically significant gene-tree conflict, particularly at deep nodes. Our results demonstrate that the evolutionary history of Chinese Diospyros has been likely shaped by deep ILS-a probable genomic signature of rapid early radiation-alongside localized ancient hybridization, most prominently within the morphologically diverse Asian clade F. Recent gene flow appears to have played a limited role, although the relative contributions of ILS and introgression remain challenging to fully disentangle. These findings provide insights into the drivers of cytonuclear discordance and offer a robust phylogenetic framework for understanding the mechanistic role of ILS in diversification, with implications for adaptive radiation dynamics in species-rich tropical lineages.
Claws are strongly sclerotised elements of tardigrade exoskeleton of a great phylogenetic and taxonomic importance. Although several general claw curvatures and anatomies can be distinguished within Eutardigrada, some more subtle differences in claw architecture have evaded the attention of taxonomists and have caused profound errors in species classification. Our study exposes a particularly deceitful morphotype and has widespread consequences for parachelan systematics, affecting two of the three major superfamilies in the order. Specifically, we analysed integratively 26 populations representing the Ursulinius cameruni complex from India and multiple locations in Australasia. Our genetic and morphological analyses demonstrate that this evolutionary lineage does not belong in Isohypsibioidea, but in Hypsibioidea. Moreover, some other taxa previously classified in different hypsibioid families are transferred to the new lineage. Specifically, Synonyxidae fam. nov. and Synonyxgen. nov. are established to accommodate the unique claw and cuticular morphotype of the Ursulinius cameruni complex. Also, Synonyx panjurliisp. nov., the type species for the new genus, is described from India, and two further hypsibioidean species are transferred from other genera to Synonyxgen. nov.: S. antonovaecomb. nov. (formerly Hypsibiidae: Hypsibius) and S. gibbosuscomb. nov. (formerly Acutuncidae: Mixibius). All these systematic changes clearly reflect the difficulties associated with a proper interpretation of claw structure in this peculiar phylogenetic linage. The evolution of Synonyxidae fam. nov. in Hypsibioidea is discussed in detail. Additionally, we elaborate on the taxonomic status and composition of Mixibius.
